1. Field of the Invention
The present invention relates to a header pipe that is employed in a condenser for a heat exchanger, a serpentine-type evaporator and the like, and is formed by shaping a flat plate material in the shape of a circular tube. It also relates to an apparatus employed for manufacturing this header pipe.
2. Description of the Related Art
Header pipes in the prior art (i.e., the header pipe for a heat exchanger disclosed in Japanese Unexamined Patent Publication No. H7-178486, for instance) are manufactured to form a header tank in the shape of a circular tube. A raw material (brazing sheet) in the form of a flat plate is fed in its lengthwise direction with a specific pitch. Tube insertion holes are sequentially formed in the material, and the material is gradually rolled while it is being fed.
To describe the manufacturing processes for manufacturing this header pipe in a more specific manner, inclined surfaces are formed on both side edges before the brazing sheet is rolled. Insertion holes for inserting partitioning plates and coupling holes for linking the intake/outlet coupling are formed in the brazing sheet. The entire brazing sheet is bent to form a rough U-shape after bending both side edges of the brazing sheet slightly and the insertion holes for inserting tubes are formed in this state. The brazing sheet is then bent to form a tubular shape, and inclined surfaces at the two side edges are abutted. Also, he brazing sheet is cut to a specific length with a cutter to form a header pipe.
With the header pipe described above, the inclined surfaces are provided at the two side edges of the brazing sheet in order to seal the pipe, and an ample bonding margin is obtained from using the inclined surfaces. However, level misalignment will occur at the abutted area if a force is applied in a direction in which the two inclined surfaces are abutted. In addition, because of the inclined surfaces, it is necessary to first roll one of the side edge portions of the brazing sheet and then to roll the other side edge portion in a final process in order to form a tubular header pipe. It has been learned through experience that this type of sequential bending results in level misalignment between the two side edge portions.
One possible solution is to provide a mandrel to ensure that no misalignment can occur in the abutted area. However, it is obvious that providing a mandrel will necessitate the use of larger dies, and will result in an increase in facilities cost. Development of a header tank and an apparatus for manufacturing the header tank that can solve this problem of misalignment in the abutted area without having to use a mandrel is desirable.
In the prior art, defective brazing is prevented by securing a sufficient brazing margin by providing the inclined surfaces on the side edge portions. It is necessary in developing a header pipe, such as described above, to give full consideration as to how the header pipe should be structured in order to assure reliable brazing.